The present invention relates to room temperature vulcanizable silicone rubber compositions and more particularly the present invention relates to self-bonding RTV silicone rubber compositions.
RTV silicone rubber compositions have been known for some time (RTV stands for Room Temperature Vulcanizable). An early type of one-component RTV silicone rubber composition has as its basic ingredients, a silanol terminated diorganopolysiloxane polymer, and acyloxy functional silane cross-linking agent and a metal salt of a carboxylic acid as a curing promoter. The composition may also contain other additives which may modify or vary the properties of the uncured and cured composition as desired. An example of such additives are fillers, heat stabilizers, flame retardant additives, etc.
One especially useful additive for such compositions was a self-bonding additive. The self-bonding additive permitted the silicone composition to be applied to substrates without the use of a primer and the composition would cure to a silicone elastomer with good self-bonding properties to the underlying substrate; that is, in most cases, the composition would rupture rather than the bond rupturing first. This is referred to as cohesive failure versus adhesive failure.
Accordingly, it was highly desirable to have a self-bonding one-component RTV composition which would result in cohesive failure of the composition rather than adhesive failure since that would mean that the composition would rupture before the bond between the composition and the substrate ruptured. One example of such a self-bonding additive is for instance to be found disclosed in Kulpa U.S. Pat. No. 3,296,161 which is hereby incorporated by reference. This patent discloses diacyloxydialkoxy silanes as self-bonding additives for acyloxy functional one-component RTV compositions.
The advantage of such self-bonding additives is obvious; that is they eliminate the need for a primer and thus they eliminate additional steps in applying the composition. This is especially desirable since the elimination of an additional step of applying the composition decreases the labor costs and thus decreases the over-all costs of utilizing the composition. Such self-bonding additives as disclosed in the Kulpa patent resulted in acyloxy functional compositions having self-bonding properties with cohesive failure to various types of substrates, and particularly to glass, ceramic, plastic and metallic substrates. Such self-bonding additives also gave good self-bonding properties to masonry substrates such as concrete, although the compositions in general do not tend to adhere as well to concrete substrates as they adhere to other types of substrates.
One-component RTV compositions with various types of functional cross-linking agents such as amine cross-linking agents, ketoxime cross-linking agents, amide cross-lining agents, etc., as well as acyloxy functional cross-linking agents are known. One new development in this area was the development of acyloxy functional cross-linking agents in which the acyloxy group has from 5-30 carbon atoms and was most preferably 2-ethylhexanoyloxy; a preferable cross-linking agent being methyl tris(2-ethylhexanoyloxy)silane. Such RTVs were desirable in that they did not give off as pungent an odor as the lower acyloxy functional RTVs and are not as corrosive. The lower acyloxy functional RTVs have as their basic cross-linking agent methyltriacetoxy silane which upon cure of the composition releases acetic acid which has a pungent odor and tends to be corrosive. Accordingly, for the above reasons the 2-ethylhexanoyloxy silane functional RTV's were desirable. However, it was necessary to develop self-bonding additives for such compositions since the traditional self-bonding additives were not altogether satisfactory.
An example of self-bonding additives for such compositions, is for instance to be found disclosed in Mitchell, et al U.S. Pat. No. 4,273,648 which is hereby incorporated by reference. This patent discloses silyl maleates, fumarates, succinates and discloses maleate functional polysiloxanes, fumarate functional polysiloxanes, and succinate functional polysiloxanes as self-bonding additives for such acyloxy functional one-component RTV compositions. However, it was found that such compositions did not have good shelf stability. Accordingly, one method of improving the shelf stability of such compositions was to pre-react the 2-ethylhexanoyloxy functional silane cross-linking agent with the self-bonding additives before it was incorporated into the composition. By such pre-reaction, it was found that the composition had good self-bonding properties as well as good shelf stability. An example of the disclosure of such pre-reaction to enhance shelf stability is to be found in the Dziark et al Ser. No. 52,042.
An example of another self-bonding additive that may be utilized in such compositions is the silyl isocyanurates of Beers U.S. Pat. No. 4,257,932. Such silyl isocyanurates are also desirable self-bonding additives for alkoxy functional one-component RTV systems as can be noted from the disclosure of Beers, U.S. Pat. No. 4,100,129 which is incorporated by reference.
These self-bonding additives work very well for the systems for which they were designed. However, there is continuing work being done in developing new and novel RTV systems so as to gain various advantages over prior RTV systems. One is the development of novel dimedone functional one-component RTV systems, as for instance, can be seen from the disclosure of Cella U.S. Pat. No. 4,223,122, Cella U.S. Pat. No. 4,176,111, Cella U.S. Pat. No. 4,176,112 and Cella U.S. Pat. No. 4,238,401. These patents disclose various types of dimedone functional RTV systems. The advantage of such dimedone systems is that they are non-corrosive and cure very quickly as well as having no unpleasant odor. However, it was found that such dimedone RTV systems had very poor bonding properties to substrates such as metallic substrates, plastic substrates, glass substrates and masonry substrates without the use of primers. Accordingly, it became highly desirable to develop self-bonding additives or adhesion promoters for such compositions. One example of such self-bonding additives is the dialkoxydi-dimedone functional silane adhesion promoters of Lampe et al, Docket 60-SI-347 which is filed on the same date as the present case. This patent application discloses that the traditional adhesion promoters which were utilized with acyloxy functional RTV's were found not to be especially desirable for dimedone functional RTV systems. Accordingly, the self-bonding additive of that disclosure was developed and utilized with dimedone systems so as to give the dimedone functional RTV systems good self-bonding properties to various substrates. Thus unexpectedly it has been found that when certain self-bonding additives are utilized in higher concentrations than was previously utilized for one-component RTV acyloxy functional RTV systems, that these adhesion promoters give good self-bonding properties to the known dimedone functional RTV systems.
Accordingly, it is one object of the present invention to provide for adhesion promoters for dimedone functional RTV systems.
It is an additional object of the present invention to provide silyl maleates, silyl fumarates, silyl succinates and silyl isocyanurates self-bonding additives for dimedone functional RTV systems.
It is still an additional object of the present invention to utilize silyl maleates, silyl fumarates, silyl succinates and silyl isocyanurates at higher levels of concentration than previously used so that such adhesion promoters will function effectively as self-bonding additives in dimedone functional RTV systems.
It is yet an additional object of the present invention to provide for a pre-reacted adhesion promoter, cross-linking agent mixture in a dimedone one-component RTV system with good shelf stability.
It is yet an additional object of the present invention to provide a process for producing a shelf-stable dimedone functional RTV system which is self-bonding.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.